A building is a closed boundary system. The purpose of a building is to provide shelter and services, such as a comfortable space, fresh air, water, and lighting. The degree to which these services are needed depends on the use and occupancy of the spaces in the building. Increasing amounts of energy cannot be stored inside the building without internal temperatures rising. If the temperatures inside the building are consistent over a day, then the net energy entering or leaving the building's closed system boundary over the 24 hour period is always zero. When more energy is put into a building than it needs, the excess energy must be rejected outside the building. Typically this is in the form of heat rejected on the roof a building.
Energy is fed into the building through electrical and natural gas flow. Other utilities may also be purchased and may enter the building, such as oil, propane, steam, chilled water, and domestic water. Each of these utilities provides an energy flow into and sometimes back out of the building. Due to a temperature difference between the inside of a building and the outside, there is always a flow of heat energy across the building shell. There is a great quantity of energy that is rejected from the building via cooling towers on the rooftop that reject the heat from inside the building to the external environment. The fresh air intake and exhausts—being at different temperatures than the outside air—are another energy flow across the building's system boundary. Over a 24 hour period, the net of all these energy flows in a building must be nearly zero or else the building is warmer or cooler from one day to the next.
When energy is purchased from a utility and enters the building, it may be converted from one form to another. For example, electrical energy may be converted to rotational mechanical energy and then again into heat. Due to the law of conservation of energy, this energy can never be used or consumed—only converted from one form to another. Therefore, due to the net zero energy constraint, every kWh of energy that is purchased and brought into the building must be rejected again from the building in the same day, perhaps in another form, such as heat. The energy is typically received through electrical cables and an equivalent amount of energy goes to the external environment at the same time.
As noted above, in order to provide the services in the building to the levels required by the operational needs, energy is converted from one form to another. For example, the energy used to pump water from the basement to the top of a tall building ensures that clean water service is provided at the top of the building at adequate pressure. However, when that water runs back down the drain to the basement it possesses all the same energy that was put in by the pump, now in the form of kinetic energy in the water flowing down the drain. In another example, when more electrical energy is put into a building or space than is rejected to the environment outside the system boundary, the net energy beyond what is leaving through the shell must be removed from the building through the cooling tower on the roof or else the building space will heat up past its operationally required temperature range.
The controls used to manage energy systems in buildings today do not and are incapable of using the net energy balance across closed system boundaries as a basis for reducing energy consumption. Accordingly, there is a need for a solution in which a building's systems are connected to a processing environment that does make energy balance calculations and manages existing equipment to achieve a reduced energy result.